Bacteria and Archaea

1
Bacteria and Archaea

• Diversity mainly in metabolism
• Essential for nutrient cycling
• Many pathogens symbionts
• No sexual life-cycle
• Extensive lateral gene transfer
• Several photosynthetic groups

2
Cyanobacteria

• Among the oldest fossils - often as stromatolites
• Important ecologically - especially in nitrogen
  fixation
• Oxygenic photosynthesis

3
Features

• Simple cells
• Many filamentous forms
• Usu. Mucilaginous sheath
• Some show cell-specialization
• E.g., Heterocysts for nitrogen fixation

Anabaena
Sheath
Heterocyst
4
________ photosynthesis

• A lot of energy needed to
• Photosystem I pulls electrons from ________
• Photosystem II pulls the electrons from
  _________
• PSI and PSII are chemically quite different

5
Other kinds of photosynthesis

• Green bacteria use a single reaction center
  similar to photosystem I
• Purple bacteria use a single reaction center
  similar to photosystem II
• Instead of water the electron donor is usually
  _____

6
Origin of oxygenic photosynthesis

• Possibly by ___________ bringing together two
  distinct photosystems
• Probably the most important event in the
  evolution of life!

7
Consequences of Oxygenic photosynthesis

• Unlike other electron donors, there is an
  unlimited supply of water
• Oxygen ______ to most organisms
• Cyanobacteria dominated the biosphere

8
Atmospheric evolution

• Oxygen produced was initially absorbed by
  ___________ deposits
• After about 2000 Ma atmosphere began accumulating
  oxygen
• ________ layer developed
• Permitted the origin of
• aerobic respiration

9
Review of main points

• ________ photosynthesis evolved only once (in
  cyanobacteria)
• PSII and PSI may have been acquired by horizontal
  _____ transfer
• Oxygen began accumulating in the atmosphere only
  after _____ in the oceans had been oxidized
• Modern oxygen levels arose much later

10
Sample question

• A plausible explanation for why purple sulfur
  bacteria cannot split H20 but cyanobacteria can
  is
• They are poisoned by oxygen
• They have only one photosystem and thus do not
  produce enough energy to split water
• Their two photosystems are not large enough to
  split water
• They are not photosynthetic
• They live at hydrothermal vents where there is
  not much H20.

11
Bacteria
Archaea
Eukaryotes
What happened here?
?
12
Events to explain

• Cytoskeleton
• Eukaryotic ________ (92)
• Endomembrane system nucleus
• Linear ________ w/ histones
• Mitochondria
• Meiosis and sex
• Plastids

Shared by all eukaryotes
Only some eukaryotes
13
Endocytosis/Exocytosis
Depends on membrane flexibility (sterols) and the
cytoskeleton
14
Eukaryotic flagellum92 _______ arrangement
Flagellum Long-section

Flagellum Cross-section
15
Why these characters are important

• Cytoskeleton cell motility, endocytosis/exocytosi
  s, developmental regulation, _____________
• Eukaryotic ______ Motility (cell-division)
• Endomembrane system nucleus Compartmentalizatio
  n
• Linear chromosomes with histones Bigger _______,
  rapid replication

16
Time frame

• The earliest plausible eukaryotic fossils at ____
  Ma
• Chemical evidence at 1700 Ma
• Fossils of multicellular eukaryotes (red algae)
  at 1200 Ma

17
Endosymbiotic Hypothesis

• Merezhkovsky (1906)---Reformulated and extended
  by Margulis (1967)
• Plastid descended from cyanobacteria
• Mitochondrion descended from an _____ bacterium

18
Evidence

• Double membrane
• Ultrastructurally and biochemically similar to
  bacteria
• Never form _____
• Have DNA, RNA and ________

19
nucleus
proteobacterium
Eukaryote
mitochondrion
20
Phylogenetic evidence
Bacteria
Archaea
Nucleus
Mitochondria
Which would favor endosymbiosis?
Bacteria
Archaea
Nucleus
Mitochondria